Fig. 6. Differential distribution of rols-transcripts during Drosophila embryogenesis. (A,B) Expression patterns from the enhancer-trap lines rols^P1027 and rols^P1729. (A) rols^P1027 embryo, stage 12, lateral view, focus on the interior. ß-galactosidase expression is detectable in both midgut primordia. (B) rols^P1729, embryo stage 16, lateral view, focus on the epidermis. The nuclei correspond to the positions of the epidermal muscle attachment sites (apodemes). (C) rols7 is first detected in the mesoderm at the extended germ band stage. (D) During germband retraction, the number of rols7 expressing cells increases but remains restricted mainly to the somatic mesoderm; weak, transient expression is detected in the visceral mesoderm (arrow). (E) After stage 12, the mRNA remains restricted to a subset of myoblasts derived from the somatic mesoderm. (F) Higher magnification of muscle precursors of the embryo depicted in E reveals expression surrounding one of the nuclei in a precursor. (G) Anti Mef2 stains all nuclei of the somatic mesoderm. (H) rP298 stains a subset of myoblasts (the muscle founder/precursor cells in every segment), while the unfused fusion-competent cells are not stained. (I,J) rols6 is mainly expressed during the invagination of the anterior and posterior gut primordium, and later on in the developing pharynx, the malpighian tubules (arrow) and in some ectodermal cells. (K) rols7 is expressed in a small group of mesodermal cells of the clypeolabrum. (L) rols6 is expressed in the ectoderm beneath the rols7-positive cells. (M) The rP298 enhancer trap pattern coincides with the rols7 expression pattern in the clypeolabrum. (N) sns is transcribed in a group of mesodermal cells of the clypeolabrum flanking the rols7-positive cells on the dorsal side.